And still don't understand any comparison with a NA engine, yes the S58 has a nice and strong top end, but the throttle response is far away from any NA engine in the world, especially the M's. Simplistically, that's really all there is to it - I've driven X3M and noticed both the higher threshold and slightly more lag in "normal" driving, but both of those aren't a problem if you're driving in a performance context as the engine is always under load and you're always in boost and above the threshold. S55 throttle response is greatly aided by its high compression ratio and smaller turbos (theoretically S55 is producing more natural power relative to its total output due to the higher ratio and therefore needs less help from the turbos - i.e smaller turbos), the expense of which is less objective top end power and tuning potential (which is why S58 is such a monster). The lack of a cat is good for a noticeable power gain, however, the ECU will need to be re-tuned to accommodate for the missing emissions piece (see Bama. When out of boost, S58 will take slightly longer than S55 to spool - which is usually represented by throttle response which I think you are describing above. Starting at 3 and tapering down to 2.25 (a step down like this accelerates exhaust flow helping the turbo to spool) the BBK pipe foregoes the bottleneck catalytic converter all together.
If you're driving below say 3.5k (as the above poster suggests) you will be out of the boost threshold whereas S55 is within or closer to its boost threshold. The "linear" powerband is just a byproduct of the classic big turbo formula. S58 has both a higher boost threshold and more turbo lag than S55 because of its lower compression ratio and bigger turbos. I think this turbo will make more power, but I hate to say, I am not going to be running it high enough boost or high enough redline to really see where it kicks butt. Turbo lag = the time in which the turbos themselves need to spool to reach optimal boost pressure I am going to beg and beg to get a test EFR 7064 turbo and in the mean time, I should have the test 8374 turbo from Full-Race any day and that will be bolted on and dynoed.
What's the difference between boost threshold and turbo lag?īoost threshold = the RPM at which an engine needs to be at to generate the desired boost pressure from the turbo
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